1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor light-emitting device equipped with a semiconductor light-emitting element and to a semiconductor light-emitting device.
2. Description of the Related Art
Conventionally, a semiconductor light-emitting device composed of a Group-III nitride-based compound semiconductor expressed by AlxGayIn1-x-yN (where, 0≦x≦1; 0≦y≦1; 0≦x+y≦1) has been manufactured as follows.
FIG. 7 shows a schematic block diagram of a semiconductor light-emitting device obtained by a conventional manufacturing method.
In a conventional process of manufacturing a semiconductor light-emitting device, an SiO2 film is formed on the top surface of p-GaN contact layer 46 of a semiconductor substrate having n-GaN contact layer 41, n-AlGaN clad layer 42, n-GaN guide layer 43, InGaN/GaN active layer 44, p-AlGaN electronic block layer 55, p-GaN guide layer 56, p-AlGaN clad layer 45, and p-GaN contact layer 46 successively arranged on a substrate 40. Thereafter, striped resist patterns are formed on the SiO2 film.
Next, with the resist patterns used as a mask, the SiO2 film is etched. Thereafter, the resist patterns are peeled off. With the resist pattern of an SiO2 film exposed by peeling off the resist pattern used as the mask, etching is carried out on the p-GaN contact layer 46 and p-AlGaN clad layer 45 as well as part of the p-GaN guide layer 56.
Then, in order to form the subsequent n-type electrode layer, the n-GaN contact layer 41 is removed by dry etching so as to expose a portion of the n-GaN contact layer 41. An insulation film 47 is provided to cover the surface of the semiconductor layer including the p-AlGaN clad layer 45 and the p-GaN contact layer 46 together with the resist pattern of the SiO2 film. The insulation film 47 may be either a ZrO2 film or an Al2O3 film.
Thereafter, the SiO2 film is removed together with the insulation film 47 by a hydrofluoric acid treatment. In addition, the insulation film 47 at the portion where the n-type electrode layer is later vapor-deposited is removed by dry etching and the n-GaN contact layer 41 is exposed.
Then, a p-type electrode layer 48 is provided to cover the top surface 52 of the p-GaN contact layer 46 exposed by removal of the insulation film 47. In addition, an n-type electrode layer 49 is provided on the exposed top layer of the n-GaN contact layer 41, and the substrate 40 and all of the layers are cleaved to obtain a semiconductor light-emitting device 500 (for example, see Japanese Unexamined Patent publications 2000-312051 and 2003-142769).
The conventional semiconductor light-emitting device 500 obtained in this way includes, in a semiconductor light-emitting device composed of a Group-III nitride-based compound semiconductor expressed by AlxGayIn1-x-yN (where, 0≦x≦1; 0≦y≦1; 0≦x+y≦1), substrate 40, n-GaN contact layer 41 as an n-type semiconductor layer arranged on the substrate 40, n-AlGaN clad layer 42 and n-GaN guide layer 43, InGaN/GaN active layer 44 as an active layer arranged on the n-GaN guide layer 43, p-AlGaN electronic block layer 55 which is located on the InGaN/GaN active layer 44 and serves as a p-type semiconductor layer with a mesa portion 53 protruding above the InGaN/GaN active layer 44, p-GaN guide layer 56, p-AlGaN clad layer 45 and p-GaN contact layer 46, insulation film 47 that covers the mesa portion 53 so as to expose the top surface 52 of the mesa portion 53, p-type electrode layer 48 as an electrode layer which covers the mesa portion 53 from above the insulation film 47 and electrically connects to the p-GaN contact layer 46, and an n-type electrode layer 49 which electrically connects to the n-GaN contact layer 41.
However, if a ZrO2 film is used as the insulation film 47, the ZrO2 film easily comes off because it has poor adhesion with respect to Pd/Au serving as the p-type electrode layer. On the other hand, if an Al2O3 film is used as the insulation film 47, while the Al2O3 film provides good adhesion with respect to Pd/Au serving as the p-type electrode layer, there exists a large difference between the refraction index of Al2O3 film (refraction index: 1.8) and the refraction index of p-GaN contact layer 46 (refraction index: 2.5). This excessively increases the locked-in effect of the light emitted in the InGaN/GaN active layer 44.
If the locked-in effect of the light is excessively increased, light is concentrated in the vicinity of the middle of the mesa portion 53. This makes the refraction index even higher in the vicinity of the middle of the mesa portion 53, which in turn causes generation of an undesirable transverse mode, resulting in an unstable kink level. That is, it becomes difficult to generate single-transverse-mode oscillation by optimizing the design of the width of mesa portion 53 alone.
Furthermore, although there is a method to make the Al2O3 film sufficiently thinner than the light-emitting wavelength, if the Al2O3 film is too thin, it is unable to keep the film uniform, making it impossible to maintain adhesion to Pd/Au.
Furthermore, because in the conventional method of manufacturing a semiconductor light-emitting device, when the insulation film 47 is formed, the insulation film 47 completely covers the SiO2 film and penetration of the etchant into the SiO2 film is blocked. Consequently, the lift-off yield with respect to the p-GaN contact layer 46, which is the p-type semiconductor layer, is excessively low.
In addition, because in the semiconductor light-emitting device manufactured by a conventional method, the insulation film 47 is provided only on the side surface of the mesa portion 53 and the p-type electrode layer 48 shown in FIG. 7 comes in contact with the entire top surface 52 of the mesa portion 53. Consequently, in the event that the semiconductor light-emitting device 500 is driven, as shown by the arrows, current from the p-type electrode layer 48 is likely to flow to the vicinity of the side surface of the mesa portion 53 and an electric field is concentrated at the edge portion 54 of the mesa portion 53. The electric field concentration at the edge portion 54 of the mesa portion 53 may damage the semiconductor light-emitting device 500.